<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>
    <style>
        * {
            margin: 0;
            padding: 0;
            box-sizing: border-box;
        }
        @media screen and (min-width: 1200px) {
            html {
                font-size: calc(625% * 4.8)
            }
        }
        @media screen and (min-width: 800px) and (max-width: 1200px) {
            html {
                font-size: calc(625% * 3.6)
            }
        }
        @media screen and (max-width: 800px) {
            html {
                font-size: calc(625% * 2.4)
            }
        }
        header ,footer {
            width: 0.2rem;
            height: 0.2rem;
            background: red;
            font-size: 0.1rem;
        }
        section {
            width: 0.5rem;
            height: 0.5rem;
            background: blue;
            font-size: 0.1rem;
        }

    </style>
</head>
<body>
    <div>
        <header>header</header>
        <section>section</section>
        <footer>footer</footer>
    </div>
</body>
</html>